Method and a system for controlling tension of paper and foil webs

ABSTRACT

In connection with the unreeling of a paper or foil web from a supply reel, e.g. in a flowpacking machine, it is well known to move the web through an adjustment station for maintaining a constant tension of the web in the outer length thereof. Normally, this is achieved by the use of a synchronously driven unreeling roller partially entwined by the web and a system for adjusting the degree of entwining based on a current detection of the web tension. With the invention this is simplified by driving the unreeling roller with a peripheral speed noticeably higher than the web speed, whereby it is possible with a suitable angle of entwining to achieve both a relatively low web tension and an automatically self-adjusting, constant web tension. By virtue of the associated, rather low dynamic friction between the roller and the web, it is even possible to effectively control or maintain the lateral positioning of the web merely by the use of simple abutments for co-operation with the side edges of the web.

The present invention relates to a method and a system for controlling amaterial web, preferably of paper or plastic and in particular inconnection with the packaging of products such as edible ice products,whereby at least one web is guided in an S-configuration over a set ofguiding rollers in order to achieve a stabilized web tension.

In connection with a continuous advancing of a paper web—from unreelingto working or handling—in, for example, packaging machines for flowpacking it is known to regulate the tension of the web in order toensure a well defined longitudinal folding of the web, yet also to avoidthat the guiding edges used for such a folding exhibit a cutting effector even cause a rupture of the web, while a stabilized tension of theweb also contributes to ensuring a desired uniformity of the finalproducts.

For the folding it is important that the paper web is drawn over thefolding edges with a sufficient tension to ensure that a longitudinalfolding will take place, but without the tension being so high that theweb is ruptured as a consequence of the folding edges being turned intocutting edges. Likewise it is important that the web be held correctlypositioned in the lateral direction relative to the folding edges inorder to ensure the desired folding profile relative to imprint detailson the wrapping web.

The paper web is advanced in being pulled through the packaging linefrom the outer end of the web, by suitable advancing means such as drawrollers.

The tension in the web occurs by virtue of the web being pulledoutwardly from a tension adjustment system, in which it is exposed to acontrollable friction, based on a current detection of the web tension.In the adjustment system the web is guided about a synchronouslyrotating friction roller with an adjustable deflection angle, the web aspaid out from this roller being guided about a delivery roller in theform of a dancing roller, the position of which is controllable foradjustment of the said deflection angle of the web. When the frictionroller is driven with a peripheral speed corresponding to the movingspeed of the web, a well defined frictional engagement is establishedbetween the web and the roller surface, given by the particular frictioncoefficient, the deflection angle and the pressure of the web againstthe roller surface. If for some reason a rising or falling web tensionoccurs, such a change may be return adjusted by causing the dancingroller to change its position for changing the said deflection angle ofthe web for a corresponding decreasing or increasing of the web frictionagainst the roller, until the tension is detected to be normal.

In principle, all this functions well in practice, but the requirementof both a web tension detector and a moving system for the said dancingroller is a complication, and another problem is that in general the webtension has to be relatively high, higher than optimally desirable.

There is an associated, different problem, viz. with respect to thecorrect positioning of the web in the transverse direction. It is wellknown that in connection with the advancing of web materials via guidingrollers it is almost impossible to effect a lateral adjustment bymechanical abutment means in case of small changes of the web directionat the intake end, so it is required, moreover, to use detection meansfor detecting lateral displacements of the web and, controlled thereby,means for compensation adjustment of a roller for achieving an accuratelateral positioning of the paid out web, this being a significantadditional and expensive complication. The problem is due to the factthat in case of a noticeable friction between a web material and asupport surface therefor it is not possible to subject the web to aneffective lateral displacement just by applying pressure to a side edgeof the web, viz. when the web itself is not sufficiently stiff to beable to transfer the required pressure to the whole width of the web forovercoming the said friction-with the support surface.

In plural lane packaging systems, more webs are moved in parallelthrough the packing machine, such that packing can be effected in aplurality of lanes for increasing the overall capacity of the system.These webs, which are advanced with the same speed, are handled bycommon friction and pay-out rollers and are also moved through a commontension adjustment station. Thus, the handling of the webs in plurallane systems is not particularly complicated due to the additional webs.However, problems may arise in case of production disturbances impartingchanges in the tension of the single webs, and besides, the plural lanesystem is limited to the handling of the same products in all thepackaging lanes.

On this background, it is the purpose of the invention to provide amethod and an associated system for adjusting the tension of a paper orsheet web to a relatively low tension level. Moreover, it is desired toprovide a method and a system that will be well suited for individualcontrol of the webs in plural lane packing machines.

Basically, the invention is characterized in that the friction roller inthe web tension adjustment station is driven with a peripheral speedwhich is substantially higher than the advancing speed of the web, suchthat a sliding friction is established between the web and the frictionroller.

With the invention, an entirely novel principle for the adjustment ofthe tension in a paper or sheet web has been provided.

Inasfar as the friction roller is driven with a noticeably higher speed,the web will be subjected to an “auxiliary drive” due to the friction,but now it is no longer the static friction, but a considerably lowerdynamical friction by the provoked marked sliding between the elements.Accordingly, a drop in tension in the paid out web will occur across thefriction roller, compared to the tension at the intake side, resultingin a decreased tension in the web as advanced through the folding tools,whereby the risk of damaging the web by these tools will be loweredconsiderably.

Moreover, the sliding engagement will condition a self adjusting effectwith respect to the web tension, such that the adjustment system willnot have to include special sensor or controlling units. Should the webtension decrease, the web will be pulled against the friction rollerwith a lower force, whereby the sliding friction and therewith theauxiliary drive effect of the friction roller will decrease. For a lowerauxiliary drive effect of the friction roller, the said tension reducingeffect on the web will also be decreased, whereby the original tensionin the web will be reestablished automatically. Correspondingly, theauxiliary drive will be strengthened if the web tension tends to rise,this primarily referring to the tension in the web stretch between theweb supply reel and the adjustment system, as the web is unreeled. Thus,the pulling off of the web will be effected with an increasing force,but in such a manner that the increased tension will not be transferredto the web length delivered from the adjustment system.

Thus, with a system according to the invention it is not a requirementto be able to change the deflection angle about the friction roller inorder to adjust the web tension. The pay-out roller arranged inconnection with the friction roller, need not be dynamically movablyarranged, although it will of course still be an option that it could bearranged as a dancing roller in order to still enable a change of thedeflection angle. However, it should be position adjustable, viz. to acorrect position relative to the actual friction coefficient.

The disclosed principle of the invention is also well suited for use ina plural lane packaging machine, where more webs are advanced inparallel, inasfar as the tension of the single webs as handled by commonfriction and pay-out rollers is individually self adjusting, implyingallowable variations of the material structure and thickness etc. of thepaper webs, without this affecting the quality of the finished productsor giving rise to production disturbances. The sliding friction in theadjustment system moreover provides for the advantage that the webs canpass the same friction roller, even if the advancing speeds of the websare not identical. This results in a far greater production flexibilityof the plural lane packing machines.

Also, it will be possible to pack different sizes and/or types ofproducts on the different lines.

If a further adjustment possibility is desired, a common guiding rollerin a plural lane system can be arranged as a dancing roller in a movablesuspension. It will also be possible to use individual pay-out rollersfor each of the lines, such that the deflection angles can be adjustedindividually.

In connection with the invention there is another aspect of such asignificance that in some connections it may even overshadow the tensionadjustment, viz. relating to the said required guiding or maintaining ofthe lateral location of the material web.

As mentioned, the invention provides for changed friction conditions inconnection with the disclosed auxiliary drive for the web, but a reduceddriving or holding friction will apply in general for the frictionalengagement, i.e. also in the transverse direction. Therewith, it iscorrespondingly much easier to effect a provoked lateral displacement orside anchoring of the web. Already for a moderate lateral stiffness ofthe web the force required for this purpose can be established solelywith the use of simple side edge abutments, this denoting a greatsimplification.

It should be mentioned that in connection with the guiding of yarn, seeGB 2,078,792, it is known to make use of a yarn reversing roller drivenwith a peripheral speed which is bigger or smaller than the speed of theyarn, the yarn being guided laterally to and fro along the roller inorder to be reeled onto an elongated yarn bobbin. The problems here infocus relate to the tension conditions in the triangular patternoperatively described by the yarn, when the latter is paid out from afixedly mounted flange wheel and, spaced therefrom, is guided to and froalong the said reversing roller. Problems in that respect are irrelevantfor the present invention, and there is not disclosed anything about theadvancing of web structures, nor about conditions for choosing betweenthe said higher and lower peripheral speed or about any qualified choicewith respect to the degree of surrounding about the reversing roller.

In the following the invention is described in more detail withreference to the drawing, in which:

FIG. 1 is a schematic view of an adjustment system according to theinvention, for controlling a paper web;

FIGS. 2 and 3 show different embodiments of means for positioning of apaper web on a roller; and

FIG. 4 illustrates an embodiment of the invention in connection with aplural lane system.

In FIG. 1, an adjustment system according to the invention is shown, inwhich a paper web 1 is guided through an inlet area 1 a, about afriction roller 2 with a deflection angle w, further through an outletarea 1 b and over a web reversing roller 4. The further pay-out 1 ctakes place over a guiding roller 6 to non-illustrated working unitssuch as folding tools. The paper web 1 is pulled through the tensionadjustment system and the other handling and working units by means of amain pulling action represented by the arrow T. The associated maindrive is arranged at the outer end of the web stretch 1 c and is adaptedto advance the web 1 with a speed vb. The friction roller 2 is connectedwith driving means driving this roller with a peripheral speed vr, whichis substantially higher than the web speed vb.

The paper web is drawn off from a supply which offers a certainresistance R against the drawing off, this resistance normally beingnon-constant. If the resistance increases, the pull T will cause the web1 to be pressed harder against the friction roller 2, whereby the latterwill increase its function as an auxiliary drive such that the tensionin the web stretch 1 a will increase, but be held constant in thestretches 1 b and 1 c. The attainment of this constancy will be a matterof selecting a suitable deflection angle w, and as indicated in dottedlines the web reversing roller 4 can be movably mounted such that it canbe positioned for defining a desired deflection angle all according tothe friction coefficient between the web and the friction roller 2. Thiscan be considered analogously with the movement of the said dancingroller in conventional adjustment systems, but with the markeddifference that with the invention the adjustment is static and notnecessarily dynamic for achieving a constant tension in the web lengthic.

If for other reasons a tension change occurs in the web length 1 c, theeffect will be quite the same, viz. that against the resistance R atension change will occur, which, when increased, will intensify theauxiliary drive of the friction roller 2, while when decreased it willweaken the auxiliary drive, such that in both cases the change oftension will be counteracted.

The sliding, dynamical advancing friction between the web 1 and thefriction roller 2 will imply that the friction also in the transversedirection is significantly lower than the static friction. This meansthat the forces required to overcome the friction and correct thetransverse location of the web on the friction roller 2 are sorelatively weak that in practice it is possible to apply such transverseforces directly to the edges of the web, without any hazard of damagingthe web.

In order to utilize this for an effective transverse stabilization ofthe web, the friction roller may be provided with annular radialprojections 6, as shown in FIG. 2. These annular ribs can be madeintegral with the roller or as ring members to be tightened to theroller. The latter embodiment has the advantage that the ribs may bemanually moved according to the width of the web to be handled.

An alternative embodiment of these positioning means is shown in FIG. 3.Here, the two lateral guiding members 8 are placed in connection withthe friction roller 2, but without rotating therewith. Thus, they arefreely adjustable in the axial direction of the roller 2 for lateralpositioning of the paper web 1.

FIG. 4 shows a system for controlling a number of paper webs 1,1′ laidabout the same friction roller 2. Because the latter is rotated with aperipheral speed vr, which is noticeably higher than any one of the webvelocities vb,vb′ of the paper webs 1,1′, there will always be a slidingfriction between the friction roller 2 and these webs. Thus, the slidingfriction is established even when the velocities vb and vb′ are notequal.

As further apparent from FIG. 4, in a preferred embodiment of theinvention it is chosen to use individual, adjustable web reversingrollers 4, 4′ in order to take advantage of the associated additionaladjustment possibility.

The invention is not limited to use in connection with tensionadjustment of paper webs in packaging machines. Thus, the method and theassociated system according to the invention may well be used fortension and positioning control of different types of material webs suchas plastic sheet, conveyor belts and the like, where the invention mayoffer the same advantages.

In principle, the web reversing roller 4 could just as well be used forco-operation with the inlet stretch 1 a.

What is claimed is:
 1. A method of providing constant tension in apaid-out stretch of web material in a flow-packing machine, whereby saidweb material is supplied with a variable tension from a supply source toa web tension adjusting station from which said web material is pulledout, said web material partly surrounding a rotatably driven frictionroller operating as an auxiliary driving means on said web material andhaving an angle of deflection determined by the location of anadjustable control roller, said method comprising the steps of: rotatingsaid friction roller with a peripheral speed directed in the pay-outdirection, said peripheral speed being substantially higher than theadvancing speed of said web material; and selecting an angular positionof said control roller in accordance with the friction coefficientbetween said web material and said friction roller for producing anincrease in web tension by an associated increase of web pressureagainst said friction roller, said increase in web tension automaticallyresulting in an increased dynamic friction between said friction rollerand said web material to increase the auxiliary driving effect upon saidweb material so as to maintain substantially constant web tension andincrease the force with which said web material is pulled from saidsupply source.
 2. A method according to claim 1, further comprising thestep of stabilizing the transverse position of said web material on saidfriction roller by engaging the side edges of said web material withguide means.
 3. A method according to claim 1, wherein said web materialis composed of a paper material.
 4. A method according to claim 1,wherein said material web is composed of foil material.
 5. Aflow-packing apparatus having means for advancing a single line of webmaterial from a web supply reel at an advancing speed to a deliverystation and producing a web tension during the advancing thereof, saidapparatus comprising; a web tension adjusting station positionedintermediate of said supply reel and said delivery station including arotatably driven friction roller in frictional engagement with said webmaterial for automatically controlling and maintaining substantiallyconstant web tension, and an adjustable web diversion roller fordetermining the angle of deflection of said web material about saidfriction roller; and wherein said friction roller is driven at aperipheral speed substantially higher than the advancing speed of saidweb material.
 6. An apparatus according to claim 5, wherein saidfriction roller includes abutment means for lateral positioning said webmaterial and having contact surfaces positioned proximate the area ofengagement between said web material and said friction roller forguiding engagement with the side edges of said web material.
 7. Anapparatus according to claim 6, wherein said abutment means arelaterally displaceable in the axial direction of said friction roller.8. An apparatus according to claim 6, wherein said abutment meansinclude annular radial projections axially positioned on said frictionroller.
 9. An apparatus according to claim 8, wherein said annularradial projections are laterally displaceable.
 10. An apparatusaccording to claim 5, wherein the position of said diversion roller isfixed.
 11. An apparatus according to claim 5 comprising at least twoadvancing lines of web material, wherein said advancing lines are indynamic frictional engagement with said friction roller, irrespective ofpossible different speeds of said at least two advancing lines of webmaterial.
 12. An apparatus according to claim 5 comprising at least twoadvancing lines of web material, wherein said advancing lines are indynamic frictional engagement with said friction roller, irrespective ofindividual deflection angles of said at least two advancing lines of webmaterial about said friction roller.